Fluid operative system and apparatus



Aug. 13, 1957 A. R. LARDIN FLUID OPERATIVE SYSTEM AND APPARATUS 3 Sheets-Sheet l Filed Sept. 15, 41953 l mlm/rm ARTHUR R-LARDIN HIS ATTORNEY Aug. 13, 1957 A. R. LARDIN FLUID OPERATIVE SYSTEM AND APPARATUS 5 Sheets-Sheet 2 Filed Sept. 15. 1955 INVENTOIL ARTHUR RLADIN HIS ATTORNEY Aug. 13, 1957 A. R. LARDIN 2,802,338

FLUID OPERATIVE SYSTEM AND APPARATUS Filed sept. 15, 1955 3 Sheets-Sheet 5 |11 il 90 @s i lo a 4o s g 70 5 w eo 67 53 U y l 22 IN VEN TR.

ARTHURRLARDIN Hss ATTQRNEY State had `2,302,338 FLUID oPERATivE sYsrnM AND APPARATUS Application September 15, 1953, Serial No. 380,245

Claims. (Cl. titl-97) This invention relates to fluid power systems and more especially to apparatus for use in the same.

An object of my invention is the provision of a practical and reliable fluid power system having sequentially operative fluid motors therein for different operating functions.

Another object of my invention is that of providing a simple and effective fluid power system wherein a plurality of fluid motors achieve sequential operation in a thoroughly satisfactory manner as from a single source of pressure uid supply.

Another object of this invention is the provision of an eicient and reliable pump operated liuid power system wherein a plurality of fluid piston motors are sequentially operable on the fluid supply for effectively achieving different outputs of power.

A further object of my invention is the provision of a @tit practical and reliable fluid motor assembly wherein a plurality of fluid motors are effectively controlled for operation in sequence.

A still further object of this invention is that of providing a simple and compact fluid motor assembly having p a plurality of piston motors therein which are operable relative to each other in sequential cycles.

Other objects of my invention in part will be obvious.V

Figure 2 is a transverse section of the fluid motor unit,

taken along the line A-A of Figure 1, and representing certain features of a detent in the unit;

Figure 3 is a longitudinal section of the motor unit, corresponding to `Figure l and representing top stroke position of operation; l

Figure 4 schematically represents a fluid power system including the motor unit of the preceding figures, the sys- `tem being set for operating the motor unit from Figure `l to Figure 3 position;

Figure 5 illustrates the system of Figure 4 reset to operate the motor unit from Figure 3 to Figure l position;

Figure 6 represents a neutral position of this same system; and

Figure 7 is a longitudinal section of a metering valve which I prefer to employ in conjunction with operation of my multiple fluid motor system.

As conducive to aclearer understanding of certain features of my invention, it may be noted at this point that uid motors and systems including these motors are in ever growing demand for performing any of a wide variety of particular functions. Frequently, in this connection, it becomes important to employ a plurality of motors for achieving different functions and in this to arrest one of the motors relative to the operation of another so as to establish an operation sequence. Among the examples of possible uses for sequence controlled fluid motors is that ofemploying one of the motors for raising and lowering a press head while another motor operates in sequence to move a body such as metal work or a receptacle to and from a point where the head comes down and seats. In another category of possible uses is that of employing a fluid motor for raising and lowering retractible landing gear of an aeroplane, and using another motor for operating a locking mechanism to hold and release the gear at the inner or retracted position. There are, of course, many other possible uses for sequence `controlled apparatus and systems, the above being intended merely as illustrative.

Some fewtypes of motor sequence control systems are `known `inthe prior art, but for the most part these amount to hydraulic or other lluid operated systems which include motors and shut-.olf valves for controlling the motor sequence. Many of these depend solely upon manual operation of the valves and, accordingly, produce no automatically attained sequence. There are other heretofore known` systems in which the operation of sequence control equipment is unduly cumbersome and expensive, to say nothing of the cost of installation and maintenance iuherent in the use of the equipment. In still other sequence control systems, as `heretofore known, the very nature of the apparatus, including the vast amount of control equipment necessary to operation, eliminates all possibility of `embodying the apparatus in compact form such as for those instances where a compact installation is most esr sential.

An outstanding object of my invention, accordingly, is the provision of uid motors having a simple, compact and reliable automatic sequence control as an `incident to their operation, and which are well suited for operation `on pressure fluid supply and amenable to easy control of the supply for starting and stopping.

Referring now more particularlyto the practice of my invention, I employ several uid motors and control `their sequence of operation bydetent means which for example alternately blocks operation of one ofthe motors while the other is operating. In this,` the motors themselves importantly control the movement of the detent means from blocking position to unblocking position, thus to assure their own operating sequence. In certain instances, I find advantage in using the several motors for sequentially driving separate loads. There are other occasions though where for example I employ one of the sequentially operated motors for intermittently powering a load, `and another` of the motors free of any load except for `operating the detent means.

In the embodiment of my invention disclosed in the accompanying drawing (see particularly Fig. l), I provide operation control apparatus which includes a motor,

`such as a primary motor lil, and another motor, such as a secondary motor dil, controlled for operation in sequence `by detent means. The `primary motor for example is rendered motive by hydraulic fluid delivered under pressure `from a suitable source of supply, such as from a hydraulic pump 50. In further particular, the fluid primary motor 1t) comprises a cylinder, illustratively as provided by a cup-shaped metal casing ll closed off at the open end by an included end plate 12. Along the longitudinal axis of the primary motor cylinder there is a piston rod 13, this extending through an opening 14 centrally disposed in the end plate 12 and through an opposite centrally disposed opening 15 at the other end of `the cylinder. The walls of the cylinder are an -Ztl to the exterior.

piston stroke.

'primary motor is to operate.

a multiple seal around the rod at each of the openings,

such as the double seal provided by rings 16 and 17 seated in longitudinally spaced annular recesses in the wall of opening 14 or by rings 1S and 19 in similar recesses in the wall of opening 15.

The fluid primary motor also includes a piston 20 4for displacement by the operating fluid supplied to the primary motor cylinder. This piston conveniently is pinned to the shaft or rod 13 by a pin 1-9 extending through aligned openings laterally of the piston and rod and secured in place as by press lit. There are openings 21 and 22 (see Fig. 2) for ingress and egress of 'uid at opposite ends of the primary ymotor cylinder,

these for connecting the opposite sides of the iiuid piston The piston 20 advantageously has annular flanges 20a and 20h adjacent to the opposite pressure faces thereof and closing olf these `faces from each other by fitting within substantially close tolerances to theinner wall surface of the primary motor cylinder. Between-these flanges, and in a recess formed by the same-with the main body of the piston 20, is asealing ring 23 or other suitable packing material to arrest uid which may otherwise pass `from one side of the motor piston to the other side. This ring conveniently rolls or slides from one of the flanges 29a and 201) to the other during reciprocation of the piston so as to lodge in front of whichever flange is behind in the direction of the A quantity of oil or other operating fluid for the primary hydraulic motor thus usually can pass by the advanced or unsealed flange to assure lubrication. The uid primary motor l@ illustratively has one of the outer ends of its piston rod 13 suited for connection with means which the motor is to operate, such for example as the press head of the citrus fruit juice extractor disclosed in my copending application for patent, Serial No. 380,244, filed September 19, 1953. This outer end of the piston rod conveniently has a longitudinal bore having threaded walls for receiving the threaded shank of an eye-headed bolt or other connector 24. The eyeshaped head of this bolt conveniently connects to a link or the like (not shown) of the apparatus which the fluid Y A nut 2S advantageously serves on the shank of the bolt, as a locking means to hold'the bolt against unscrewing. For this purpose, the nut is tightened down against the outer end of the rod 13, and may be loosened and seated again to lock the connector 24 to a newly adjusted position selected for lengthening or shortening the rod 13.

At the other outer end of piston rod 13, remote from the connector 24, I provide detent means 30 for selec- -tively arresting the operation of the primary motor 10.

This detent meansV (see Fig. 2) preferably includes -parallel links 31 and 32 for example of the same shape and size and advantageously in the form of bell-cranks -spaced'directly opposite each other so as to admit the -rod 13 and admits passage thereof lateral to the pins.

One corresponding adjacent set of effective lever ends of the bell-cranks 31 and 32 have aligned openings 31b and 321;, between which there is a detent roller 35 having an axial 'opening which is also in alignment, thus to Vreceive a bolt 36. VThe bolt 36 and a corresponding nut 36d serve to hold these ends of the bell-cranks and the roller in assembled relation so that the latter may be moved about pins 33 and 34 as a center toand from `pressure face of this piston.

restraining position relative to the piston rod 13, such as to and from the path of the corresponding outer end of the rod. The detent roller 35 preferably is so disposed relative to pins 33 and 34 as to roll along the longitudinal surface of the rod 13 when in non-restraining position. To facilitate this vrolling action, the detent roller preferably has ball bearings or some other suitable anti-friction mounting relative to bolt 36. Also, if desired, the opposite ends of the detent roller may be separated from the adjacent ends of the bell-cranks by suitable bearings or clearance to decrease friction.

The other effective lever ends of the bell-cranks 31 and 32 conveniently have aligned openings which receive the opposite ends `of a strut or spacing element 37 vfor the cranks. This spacing element for example has relatively small diameter ends as compared with its intermediate body portion which is too large to pass through the crank openings and thus affords a stop. The relatively small ends of the spacing element conveniently are upset against the outer surfaces of the cranks thus tohold the same in assembled relation. Both the detentl roller 35 and the spacing element 37 are suiciently long in the present embodiment to separate the bell-cranks onto Athe pivot pins 33 and 34 and prevent escape from this tudinal bore through the body thereof between the axial bore 2S and the annular flanges 20a and 2Gb thus to -provide a cylinder for the secondary motor 40, this cylinderV opening to the primary motor cylinder on the opposite pressure faces of the primary motor piston 13. The secondary motor piston 71 advantageously has an 'annular recess 72 receiving a packing ring 73 for'rsealing off the opposite pressure faces of the latter piston.

There is a rod 74 for the secondary motor piston, this rod for example being in two parts 74a and 74b axially disposed relative to this. pistonand extending away from the opposite pressure faces of the same. That part 74a of the rod conveniently is made integral with the corresponding recess having threaded walls on the opposite The partY '74h of the secl `ondary motor piston rod 74 slidably extends through an opening 48 in the end plate 12 and is sealed against leakage of fluid through this opening by spaced packing rings and 76 which fit into annular recesses in the opening wall. Outside and considerably beyond the plate opening 4S the piston rod component 74b has its outer end linked or otherwise operatively connected with the detent means for achieving the operation control functions hereinafter to be described. One or more links 77 conveniently serve this purpose by connecting the adjacent end of component 74h with the strut or spacing element 37. The linkV or links illustratively have their oppositerends .perforated to fit onto the strut or spacing element 37 along the length thereof between the bell-cranks 31 and 32 and to receive a pin 38. The pin 38 extends into an opening laterally through the Vend of component VV74band for example `has its ends upset to fasten the several elements together in operative relation; Y

That part of one piston rodn74lextending in the opposite'direction, namelythe part 74apasses through an .opening 47 in the cup-shaped p ortion 11 and is sealed against leakage of fluid through this opening by packing rings 78 and 79 seated in annular grooves in the opening wall. Outsideand considerably ybeyond the opening 47, the rod component.Ma-illustratively has its end con- 44 or the like offapparatus which the secondary motor 4d illustratively is used to operate. The link 44 conveniently serves to rotate a shaft 45 having a fixed axis 46, this shaft for example beingthat for tilting a fruit receiver cup to and from operative position relative to the press head of my citrus fruit juice extractor disclosed in the copending patent application hereinbefore noted.

It will be seen that the motor `assembly represented in the accompanying drawing has primary motor piston 20 andsecondary motor piston 40 so disposed as to provide faces confronting the pressure fluid for operation whether this fluid be admitted through port 21 or 22 to the primary motor cylinder and thence to the secondary motor cylinder. The interfitting pistons 20 and 71 have their respective rods 13 and 74 substantially parallel in direction for transmitting the force of the pressure fluid brought to bear upon their faces. Also, in this embodiment, the longitudinal axes of the pistons 20 and '71 are substantially parallel to enable respective operation of the pistons in a manner which will be more fully described hereinafter.

A pump t) (see Fig. 4) such as of the gear type, usually employed in my uid power system, illustratively draws oil from a reservoir 7i) to operate the primary motor 10 and the secondary motor 40. An electric motor 90 for example drives this pump as by means of a belt or chain and sprocket connection 95. On the intake side, the pump is connected with reservoir 70 by fluid supply line 51 which for example extends into the bottom of the reservoir to prevent the pumping of air. The pressure side of the pump preferably is connected to a distributing valve 66 for the fluid, the connection for example be.- ing through the casing of the valve at port 61. Inside the valve casing there is a rotary core having separate passages 65, 66 and 67 therethrough for selectively connecting the pressure side of the pump with cylinder ports 21 `or 22 of the primary `motor 10 or with the reservoir 7i). For achieving these connections, the valve 60 has ports 62, 63 and 64 through the casing thereof, the ports 62 and 64 respectively being in communication with cylinder ports 21 and 22 through conduits 54 and 55, and port 63 being in communication with the reservoir 70 through conduit 53.

The disposition of the passages in the coreof valve 6l) relative to the ports in the valve casing enables the passage 65 to be set by rotation of the core to interconnect ports 61 and 62 (see Fig. 5), passage 66 at this time being blocked by the valve casing wall against the admission or exit of fluid, and the passage 67 for this position interconnecting the ports 63V and 64. A reverse setting of the valve core also may be had by rotating the same to position where the passage 67 interconnects ports 61 and 64 (see Fig. 4), at which time passage 65 interconnects the ports 62 and 63, while passage 66 remains vblocked as before. In order to cut o both passages 65 and 67 from communication with any of the previously named ports the valve core may be rotated to neutral position (see Fig. 6) where the passage 66 interconnects the ports 61 and 63. The behavior of the fluid primary motor 10 and fluid secondary motor 4t) corresponding to the several settings of the valve will now be described.

With the pump 50 operating to draw oil from therreservoir 70 through the line 51, first assume that the valve 60 is set to the position indicated in Figure 4 and that the primary motor 10 and the secondary motor 40 `are to be actuated in a setrof upward directions beginning with the position represented in'Figure l. The pumped uid accordingly passes from the pressure side of the pump through conduit 52 to port 61 of thevalve 60 and thence through passage 67 to the port 64. From the exit side of the valve, this fluid goes through conduit 55 and enters the cylinder of primary motor 10 at port 22. Once in the primary motor cylinder, the iiuid develops a` pressure on the underneath side of the primary motor 'piston 20 `(FigureA l) and effects an upward movement of this piston. In moving upward, the piston 20 effects a displacement of the corresponding piston rod 13, by virtue of the pin connection 19. This rod 13 of the primary motor thus slides upward in Figure l through openings 14 and 15 in the primary motor cylinder. In this movement fluid seeps by the annular flange 20h of the piston and forces the packing ring 23 up against annular ilange 20a where a` positive seal is effected. The fluid behind this seal accordingly lubricates the section of the primary motor piston. The eye-shaped connector 24 transmits the force of the moving rod 13 to apparatus which the primary motor 10 is intended to drive and thus effects a driving action. During the upward motion of the primary 'motor piston 20, piston 71 of the secondary motor 40 also has its lower face exposed to the pressure huid from the pump 5t). The piston 71, however, is effectively arrested against an upward movement by virtue of the fact that its corresponding piston rod 74 is connected by link 77 to the detent means 30. In fact, the bell- `cranks 31 and 32`restrain the strut 37 and link 77, and

thus the secondary motor piston rod 74 against upward `movement by forcing the detent roller 35 downward in under the pressure of the uid admitted through the primary motor cylinder port 22. The pressure of the tluid on the corresponding face of the piston 71 actuates this piston and, accordingly, `the rod 74 thereof slides upward through openings 47 and 48 in the primary motor cylinder and exerts 'a driving action if desired as through link 43 and lever 44 on apparatus which the secondary motor 40 illustratively is used to operate. During the actuation of motor 40, the piston rod 74, as connected through link 77 and strut 37, exerts a lifting action on the adjoining ends of the bell-cranks 31 and 32 which rotates the opposite ends of the cranks and the detent roller 35 in a counter-clockwise direction (Figure l) about fixed pivots 31a and 32a. The detent roller 35 (see Fig.

3), accordingly, takes a position serving to block a reverse stroke of the primary motor piston rod 13, such as a position behind the lower end of this rod. In this new position, the detent roller for example again acts as a stop against continued upward movement of the secondary motor piston 71 such as by abutting the adjacent end of the primary motor piston rod 13.

During the upward set of operations of the primary motor 10 and secondary motor 4t) just described, port 21 in the primary motor casing is open and connected by conduit 54 (see Fig. 4) for outlet of liuid which may have remained on this side of the motors previous to operation in a reverse direction which will be described. In passing through port 21 and conduit 54, the fluid continues through port 62, passage 65 and port 63 ofthe valve 60 and then passes through conduit 53 to the supply reservoir 7i).

By resetting the Valve 6i) to position represented in Figure 5 it is possible to reverse motors 10 and 40 for operation of their pistons in a set of reverse directions. Thus, fluid drawn from reservoir 7i) through conduit 51 by the pump 5i) is supplied to this valve through conduit 52 and port 61 and from here goes through passage 65,

port 62 and conduit 54 to port 21 of the primary motor cylinder. Under these conditions fluid admitted through the port 21 exerts itself against the adjacent face of the primary motor piston 20 (see Fig. 3), but this piston is restrained against displacement underthe action of the uid by virtue of the fact that the detent roller 35 blocks .this movement. The secondary motor 40, however, -is free to operate and does so under the action of the fluid radmitted through port 21 to the adjacent face of piston `71. A downward motion of rod 74 thus accompanies the operation of this piston, and the rod serves to actuate the detent means 30. In this, component 74b of the rod pushes link 77 and the adjoining ends of bell-cranks 31 and 32 down rotating the cranks about their xed pivots 31a and 32a in a clockwise direction thus carrying detent roller 35 away from the path of rod 13 of the primary motor piston 2l). Where the secondary motor 40 also serves to actuate'apparatus such as through link 43, lever 44 and shaft 45, this apparatus illustratively undergoes a reverse action during the downward stroke of the piston 71 as compared with an upward stroke of this piston.

With the piston of the primary motor released by displacement of the detent Vroller`3` 5 away from the path of rod 13, as described, the pressure of fluid admitted ythrough the port 21 now is effective to operate the primary motor. Thus, piston 20 and'its'rod 13 slide downward in the primary motor cylinder, and the rod conveniently affords a stop for the detent roller 35 which therefore in turn arrests downward movement of the secondary motor piston 71. The primary motor 10, though, continues to operate in a downward direction, the detent roller conveniently rolling along the longitudinal surface 'of therod 13. The apparatus driven by the primary 'motor 10 as through connection with the connector 24, illustratively undergoes a reverse operation corresponding to downward movement of the piston 20 as compared `with the upward movement of this piston.

During the downward set of operations of the primary and secondary motor pistons, fluid on the advanced faces of these pistons conveniently passes through port 22 and thence through conduit 55, port 64, passage 67, port 63 vand conduit 53 into the fluid supply reservoir 70 (see Fig. 5). The downward action of piston 20 which occurs after piston 71 ceases downward operation, illustratively is arrested and reversed to the upward action by resetting the valve 60 (see Fig. 4) thus to supply lluid from the pump 50 to the primary motor cylinder port 22. By setting the valve to neutral position relative to the primary and secondary motors (see Fig. 6), that is to a position where the valve rotor passage 66 interconnects ports 61 and 63, the pump may continue running without hurtful effect upon the fluid system. vUnder the latter conditions, `iluid passes from the reservoir 'itl through conduit 51 to the intake side of the pump. This fluid is discharged from the pressure side and courses through conduit S2 and directly through port 61, passage 66 and port 63 to conduit 53, thus back to the reservoir 7i). In this posi- `tion of the valve 68, the passages 65 and 67 are effectively closed olf from operating relation with the pump and primary and secondary motors.

In the line 52 between the pump 58 and the distributing Vvalve 60, I usually provide a relief valve 88 for bleeding edly received in the hole in plate 188. The valve stem is sealed against leakage by a surrounding washer 87 `pressed to position by a laterally extending ledge thereon;

This ledge conveniently is provided by making the threadled portion 86 of smaller diameter than an adjoining cylindrical portion of the casing, the latter being immediately behind the threaded area, and the ledge being a Vtransition surface.

The iluid inlet opening 82 in plate 95 leads into the threaded opening 101 in plate litt) which in turn opens into central bore 83 of the valve 80. Within bore 83 ispositioned the longitudinally slidable plunger 84. The valve plunger is substantially conical in form, and the conical portion increases in diameter with distance back along the bore 83. Still farther back, the plunger conveniently is substantially cylindrical in shape in conformity with bore 83. Along this zone of the bore, there is lateral opening 85 through casing 81, thus to afford an outlet for lluid admitted through inlet 82 and thence to the bore.

Under normal pressure conditions, the fluid outlet opening 85 is closed by the substantially cylindrical portion of the plunger 84. This position of the plunger is main-` tained as by a ball 88 and helical spring 89 disposed in an enlargement of the cylindrical bore 83 behind the inner end of the plunger, forcing the plunger against plate 102 dening one wall of inlet opening 82. The ball advantageously is sufficiently large to be guided by the bore wall. It acts as a pressure element to apply the force of the spring to the inner end of the plunger. Also, the ball advantageously affords a bearing surface for the adjacent end of the spring for transmitting the force thereof and conveniently compensates for any eccentricity of alignment of the different diameter bore zones of bore 83. The other end of the spring preferably is seated against an adjustable support such as the inverted cup of a cup-shaped screw plug 90 having threads on the outer surface for engaging corresponding threads extending longitudinally along the wall of the bore 83. Thus, the plug 94) may be advanced or retarded, as with the aid Vof a screw driver notch 91 in the outer end surface thereof, to vary the compression of spring 89 and the force on ball 88 which in turn alters the load opposing valve plunger 84, tending to counteract displacement of the plunger by fluid under pressure in the line 52 and at the inlet opening 82.

The casing 81 illustratively is oblong to save material in product and yet house the several inside components of the meter valve in tandem along the bore 83, this bore preferably being substantially straight in axial direction from end to end of the casing. On the outside, the casing preferably is round in transverse section except for llat sides 99 to allow wrench grip.

The outlet opening of the metering valve (see Figs. 4, 5 and 6) is connected with lluid reservoir 70 by conduit 56. Thus, whenever pressure of fluid in the line 52 becomes so great as to force the valve plunger 84 backward against the action of ball 88 and spring 89 (see Fig. 7), away from the inlet and outlet openings, an admission passage develops between the conical plunger end and the adjacent cylindrical wall of the bore 83. The size of this admission passage increases with the amount of backward displacement of the plunger, which displacement is effected as a function of the pressure in line 52 to give a metering effect as applied to that quan tity of Huid which escapes through the outlet opening of the valve. In this, of course, the metering valve plunger moves back sullciently far to uncover the outlet opening to the conduit 56 which then returns the fluid to reservoir 70. In being connected into the system between the outlet side of pump 50 and the inlet side of the fluid distributing valve 60, the metering valve 80 is available for bleeding oil fluid whether it be because of excess pressure brought about by load demands imposed on either the primary motor 10 or secondary motor 40, or by stoppages imposed in the system such as in resetting the valve 60.

Thus, it will be seen that in this invention there is provided a fluid power system and apparatus for use in the same, in which the various objects noted herein together with many thoroughly practical advantages are successfully achieved. In this connection, it will be noted Vthat the several fluid motors and the apparatus for cor1- trolling their sequence of operation co-function with reliable and highly satisfactory results. Also, it will be seen that a uid power system embodying the sequence controlled motors has many practical advantages, as from the standpoint of being simple to construct and operate, by virtue of having the motors themselves initiate automatic function for controlling the sequence of motor operation.

As many possible embodiments may be made of my invention and as many changes or alterations may be made in the embodiment hereinbefore set forth, it will be understood that all matter V,described herein is to be interpreted as illustrative and not as a limitation.

I claim: t

1. A motor assembly comprising two uid motors having pistons and corresponding rods, the piston of one of said motors being slidable in a bore longitudinally through the piston of another of said motors and the rods of said pistons being substantially parallel and operative in substantially the same directions of stroke for one set of movements and then for a reverse set of movements, and detent means in driven relation to the piston rod of one of said motors and eiective with respect to one of said acts of movement for arresting the rod of said one motor by abutting the rod of said other motor until freed by the movement of such other rod and effective with respect to said set of reverse movementsl for arresting the operation of the other motor by disposition in the path of operation thereof, until driven aside by operation of the one motor.

2. A motor assembly comprising primary and secondary fluid motors including pistons and corresponding rods, and a casing forming a cylinder for reciprocation of the piston of said primary motor and alfording ports for fluid open to the opposite faces thereof, the piston of said secondary motor being slidable in a bore longitudinally through the piston of said primary motor and having opposite faces for exposure to the same tluid pressure as the adjacent piston faces, and the corresponding rods of said pistons extending through openings in the casing Wall and sealed relative to the same for reciprocation with their pistons; and detent means in driven connection with the piston rod of said secondary motor for arresting the piston rod of said secondary motor by abutting the rod of said primary motor until freed by forward movement of the same; and effective for arresting movement of the rod of the primary motor in reverse direction by disposition in the path thereof, until driven aside by operation of said secondary motor.

3. A uid power system including a source of Huid pressure; a motor assembly comprising primary and secondary uid motors for operation in a set of forward directions and then in a set of reverse directions, and detent means driven by said secondary motor and effective with respect to one of said sets of `operating directions for arresting said secondary motor, until freeing the same as an incident to operation of said primary motor, and effective with respect to said set of reverse directions for arresting the primary motor and freeing the same as an incident to operation of the secondary motor; and a iluid distributing valve for directing uid from said source of pressure to said motors to drive the same in one of the sets of directions and then in the reverse set of directions.

4. A fluid power system comprising a source of tluid pressure; a motor assembly including primary and secondary uid motors for operation in a set of forward directions and then in a set of reverse directions, and detent means effective with respect to forward operation of said motors for arresting said secondary motor, until freeing the same as an incident to operation of said primary motor, and effective with respect to said set of reverse directions for arresting the primary motor and freeing the same as an incident to operation of the secondary motor; a fluid distributing valve for directing fluid from the source of pressure to said motors to drive the same in one of said sets of directions and then in the reverse set of directions; and a fluid pressure relief valve connected between said source and distributing valve for returning fluid to said source,

5. A motor assembly comprising at least two uid motors having pistons and corresponding rods, the piston of one of said motors being slidable in a. bore longitudinally through the piston of another of said motors, and detent means in driven relation to the piston rod of one of said motors and in contact with the piston rod of the other motor for arresting forward movement of said one motor until freed by movement of the piston of said other motor and arresting reverse movement of said other motor until freed by the piston of said one.

References Cited in the le of this patent UNITED STATES PATENTS 1,807,594 Hopkins June 2, 1931 1,981,400 Tobin Nov. 20, 1934 2,130,618 Gnavi Sept. 20, 1938 2,355,916 Klafstad Aug. l5, 1944 2,622,400 Greer Dec. 23, 1952 2,644,306 Paulsen July 7, 1953 

